Austenitic paramagnetic corrosion resistant material

ABSTRACT

The alloys of the present invention provide austenitic, paramagnetic materials with high strength, ductility, and yield strength and good corrosion resistance in media with high chloride concentrations. Alloys of the present invention were developed because of the need by oilfield industries for superior materials. The alloys of the present invention may be used in drilling string components, and the tests performed demonstrate that such alloys exhibit properties balanced for very high yield strength, magnetic permeability, and corrosion resistance superior in every respect to presently available paramagnetic, high strength, corrosion resistant austenitic stainless steels.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/768,133, filed Jun. 25, 2007, now pending, which claims the benefitunder 35 U.S.C. §119(e) of U.S. Provisional Patent Application No.60/816,213, filed Jun. 23, 2006, which applications are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to austenitic, paramagnetic andcorrosion-resistant materials having high strength, yield strength, andductility for use in media with high chloride concentrations, and, moreparticularly, to steels suitable for use in non-magnetic components inoilfield technology, especially in directional drilling of oil and gaswells.

2. Description of the Related Art

High-strength materials that are paramagnetic, corrosion-resistant andwhich, for economic reasons, consist essentially of alloys of chromium,manganese, and iron are used for manufacturing chemical apparatuses, indevices for producing electrical energy, and, in particular, forcomponents, devices and equipment in oil field technology.Chromium-manganese stainless steels have been favored in the manufactureof such parts because they satisfy the requirements of non-magneticbehavior, high yield strength, and good resistance to chloride stresscorrosion cracking, all at a reasonable cost. However, increasinglyhigher demands are being placed on the chemical corrosion properties aswell as the mechanical characteristics of materials used in this manner.

In these types of stainless steels, it is indispensable for the behaviorof the material to be completely homogeneous and highly paramagnetic.For example, in cap rings of generators with high yield strength andductility, a possible low-level ferromagnetic behavior must be excludedwith utmost certainty. For measurements during drilling, in particularexploration wells in crude oil or natural gas fields, drill stems madeof materials with magnetic permeability values below about 1.02 orpossibly even less than 1.01 (using a Severn gauge) are necessary inorder to be able to follow the exact position of the bore hole and toascertain and correct deviations from its projected course.

It is furthermore necessary for devices in oil field technology anddrill stem components to have high mechanical strength, in particular ahigh yield strength at 0.2% offset, in order to achieve machinery andplant engineering advantages as well as a high degree of operationalreliability. In many cases, high fatigue strength under reversedstresses is just as important because pulsating or alternating stressesmay be present during rotation of a part and/or drill stems. Finally,the corrosion behavior of the material in aqueous media, in particularmedia having high chloride concentrations, is critically important.

As a result of the demands of recent developments in deep drillingtechnology, increasingly stricter criteria are being placed on materialsin terms of the combination of paramagnetic behavior and high yieldstrength, as well as strength, resistance to chloride-induced stresscorrosion, especially resistance to pitting corrosion (pitting), andcrevice corrosion. Some materials made from Cr—Mn—Fe alloys are knownwhich, with respect to their mechanical characteristics and corrosionbehavior, completely fulfill these requirements. However, their magneticpermeability values prevent their use in parts used in connection withmagnetic measurements and exclude their use for drill stems. On theother hand, available paramagnetic materials with good strengthcharacteristics cannot resist attacks by corrosion and, for the mostpart, paramagnetic parts with high corrosion resistance often do nothave the necessary high mechanical values.

Control of pitting corrosion resistance, is very important inmeasurement while drilling (MWD) components where, due to complexinternal geometry, mud deposits can form and produce crevices forcorrosion pits to grow. Pitting corrosion resistance of a material canbe predicted by PREN values of the material, wherein the PREN value isdefined as (wt-% Cr)+(3.3)(wt-% Mo)+(16)(Wt-% N). Pitting is a localattack that can produce penetration of a stainless steel with negligibleweight loss to the total structure. Pitting is associated with a localdiscontinuity of the passive film. It can be a mechanical imperfection,such as surface damage or inclusion, or it can be a local chemical breakdown of the film. Chloride is the most common agent for initiation ofpitting. Once a pit is formed, it in effect becomes a crevice. Thestability of the passive film with respect to resistance to pittinginitiation is controlled primary by chromium, molybdenum and nitrogen.

Use of nitrogen to improve mechanical and chemical corrosion propertiesof substantially Cr—Mn—Fe alloys is known, however, this requiresexpensive metallurgic processes operating at elevated pressure. Foreconomic reasons, Cr—Mn—Fe alloys have been developed that can beproduced without pressurized smelting or similar casting processes,i.e., at atmospheric pressure, in which a desired characteristic profileof the material is achieved using alloying technology (PCT PublicationNo. WO98/48070). For the purpose of improving corrosion resistance,these alloys have a molybdenum content of over 2%. This results inimproved pitting and crevice corrosion behavior. However, molybdenum,like chromium, is a ferrite former and can lead to unfavorable magneticcharacteristics in the material in segregation areas. While increasednickel contents stabilize the austenite, possibly in conjunction withincreased copper concentrations, it has been believed that increasednickel content may have a detrimental effect on the mechanicalcharacteristics and intensify crack initiation.

There are many alloys from the chromium-manganese austenitic stainlesssteel group that have long been known and are presently available. PCTPublication No. WO91/016469 makes an attempt to use a balancedconcentration of alloy elements to create an austenitic, antimagnetic,rust-proof steel alloy that, during hot working, has a beneficialcombination of characteristics without further tempering. EuropeanPatent No. EP-0207068 B1 suggests a process for improving mechanicalcharacteristics of paramagnetic drill string parts in which a materialis subjected to a hot and a cold forming, with the cold forming takingplace at a temperature between 100° C. and 700° C. and a degree ofdeformation of at least 5%.

More recently, U.S. Pat. No. 6,454,879 described an austenitic,paramagnetic and corrosion-resistant material comprised of carbon,silicon, chromium, manganese, nitrogen, and optionally, nickel,molybdenum, copper, boron, and carbide-forming elements. This patentteaches that levels below about 0.96 wt-% of nickel and below about 0.3wt-% copper are needed to achieve the desired degree of corrosionresistance. However, at these low levels of nickel and copper (these twoelements being austenite formers), low levels of molybdenum and/orchromium (being ferrite forming elements) must be present for a stablemetallurgical structure, and therefore this steel fails to meet thedesired level of pitting corrosion resistance.

Recent developments in deep-well drilling methods have demanded morestringent requirements on the materials and parts. These parts arerequired to operate in increasingly severe chloride environments and atthe same time the drilling is done in much deeper levels where the partsare required to have much higher yield strengths. None of the steelsdiscussed above have all of the desired properties of yield strength andpitting corrosion resistance necessary for acceptable performance underthese more exacting operating conditions.

Accordingly, although there have been advances in the field, thereremains a need in the art for alloys with a higher critical pittingpotential which can be forged to very high yield strengths whilemaintaining their paramagnetic properties, high toughness, andmicrostructures free from carbides, nitrides, and sigma and chi phaseprecipitation. The alloys of the present invention address these needsand provide further related advantages.

BRIEF SUMMARY OF THE INVENTION

In brief, the present invention is directed to austenitic, paramagneticand corrosion-resistant materials having high strength, yield strength,and ductility for use in media with high chloride concentrations. Theinvention provides alloys suitable for use in non-magnetic components inoilfield technology, especially in directional drilling of oil and gaswells.

In one embodiment, an austenitic, paramagnetic material with highstrength, ductility, and yield strength and good corrosion resistance inmedia with high chloride concentrations is provided, comprising (inwt-%): up to about 0.035 carbon; about 0.25 to about 0.75 silicon; about22.0 to about 25.0 manganese; about 0.75 to about 1.00 nitrogen; about19.0 to about 23.0 chromium; about 2.70 to about 5.00 nickel; about 1.35to about 2.00 molybdenum; about 0.35 to about 1.00 copper; about 0.002to about 0.006 boron; up to about 0.01 sulfur; up to about 0.030phosphorous; and substantially no ferrite content.

In a further embodiment, the material comprises about 2.70 to about 4.25wt-% nickel. In yet a further embodiment, the material comprises about2.75 to about 4.20 wt-% nickel. In yet a further embodiment, thematerial comprises about 3.50 to about 4.20 nickel.

In another further embodiment, the material comprises about 0.35 toabout 0.85 wt-% copper. In yet a further embodiment, the materialcomprises about 0.35 to about 0.75 wt-% copper. In yet a furtherembodiment, the material comprises about 0.50 to about 0.75 copper.

In another further embodiment, the material comprises (in wt-%): up toabout 0.030 carbon; about 0.25 to about 0.45 silicon; about 22.0 toabout 23.0 manganese; about 0.75 to about 0.90 nitrogen; about 19.0 toabout 20.0 chromium; about 2.70 to about 4.25 nickel; about 1.40 toabout 1.80 molybdenum; about 0.35 to about 0.75 copper; about 0.003 toabout 0.006 boron; up to about 0.006 sulfur; and up to about 0.025phosphorous. In yet a further embodiment, the material comprises (inwt-%): up to about 0.028 carbon; about 0.30 to about 0.45 silicon; about22.0 to about 23.0 manganese; about 0.78 to about 0.90 nitrogen; about19.0 to about 20.0 chromium; about 3.50 to about 4.20 nickel; about 1.40to about 1.75 molybdenum; about 0.50 to about 0.75 copper; about 0.003to about 0.006 boron; up to about 0.003 sulfur; and up to about 0.20phosphorous.

In another further embodiment, the material has a PREN value of greaterthan about 37. In yet a further embodiment, the material has a PRENvalue of greater than about 37 and less than about 39.

In another further embodiment, the material has a yield strength at 0.2%offset of greater than about 140 ksi. In yet a further embodiment, thematerial has a yield strength at 0.2% offset of greater than about 140ksi and less than about 190 ksi.

In another further embodiment, the material has a PREN value of greaterthan about 37 and a yield strength at 0.2% offset of greater than about140 ksi. In yet a further embodiment, the material has a PREN value ofgreater than about 37 and less than about 39 and a yield strength at0.2% offset of greater than about 140 ksi and less than about 190 ksi.

These and other aspects of the invention will be evident upon referenceto the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of theinvention. However, one skilled in the art will understand that theinvention may be practiced without these details. In other instances,well-known aspects of steel alloys have not been shown or described indetail to avoid unnecessarily obscuring descriptions of the embodimentsof the invention.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to”.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of alloys of the present invention. Thus, the appearances ofthe phrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

The present invention provides an austenitic, paramagnetic material withhigh strength, ductility, and yield strength and good corrosionresistance in media with high chloride concentrations, comprising,silicon, manganese, nitrogen, chromium, nickel, molybdenum, copper,boron, and positive amounts of carbon, sulfur, and phosphorous; thebalance including iron. The material has substantially no ferritecontent and is preferably substantially completely austenitic. Thematerial has a higher critical pitting potential than previous alloysand can be forged to very high yield strengths in sections as large as12.75 inches in diameter. The material in this form maintains itsparamagnetic properties, very high toughness, and a microstructure freefrom carbide, nitrides, and sigma and chi phase precipitation. A processfor producing the material and beneficial representative methods of useare provided.

The alloys of the present invention are produced using a cost effectivebasic electric arc furnace melting procedure. Secondary refining of thematerial utilizing the Argon-Oxygen Decarburization (AOD) processprovides precise chemistry control and uniform teeming temperatures. TheAOD process allows for low sulfur and oxygen levels resulting inexceptionally clean steel.

Oil-well drilling components made from alloys of the present inventionare manufactured by the open die forging technique, using a warm forgingprocess to achieve the desired mechanical properties. To obtain the bestcorrosion properties, alloys of the present invention are solutionannealed at 1900° F. before final forging. Materials manufactured underthese conditions have high yield strengths (>144 ksi) and PREN values(>37.00) and very good Critical Pitting Potential (400 mV in 80,000 ppmCl solution) as well as meeting the desired minimum requirements formagnetic permeability (not greater than 1.004 using a Dr. Foerstermagnetoscope (model 1.067)) and intergranular corrosion resistance perASTM 262 A (step structure only), minimum hardness (341 HBN), and notchimpact strength (122 J).

Carbon strongly contributes to austenitic formation and to stabilizationof the austenite against transformation of martensite. However, highcarbon content also leads to precipitation of chromium carbides whichleads to impaired corrosion properties, embrittlement in the alloy, anda destabilization of the austenite and possibly local martensitetransformation. This in itself can make the material partiallyferromagnetic. Higher carbon contents also lead to pitting and corrosionin chloride-containing media as well as to intergranular corrosion ofparts manufactured therefrom. Carbon also has limited solubility inaustenite and higher concentrations can lead to precipitation ofchromium carbides. Because of the negative effects of higher carbonconcentrations, alloys of the present invention do not exceed about0.035% by weight and in some embodiments carbon does not exceed about0.030 wt-%. Further embodiments of alloys of the present invention donot exceed about 0.028 wt-% carbon.

Silicon is present in the alloys of the present invention as adeoxidation element with a concentration of about 0.25 to about 0.75wt-% in some embodiments. Substantially higher contents of silicon canlead to nitride formation and to a decrease in resistance of thematerial to stress corrosion. Because silicon also has a strongferrite-forming effect, higher contents can negatively influencemagnetic permeability. Thus, some embodiments of the alloys of thepresent invention incorporate silicon in the range of 0.25 to 0.45 wt-%while other embodiments incorporate about 0.30 to about 0.45 wt-%silicon.

Manganese is added to the alloys of the present invention to increasethe solubility of nitrogen in the melted and solid phase (austenite) andto stabilize the austenite. The upper limit of manganese in alloys ofthe present invention is restricted to a maximum of about 25.0 wt-%.Manganese will form some austenite but is added primarily to stabilizethe austenite and for holding large amounts of nitrogen in solution, butin contents above about 25 wt-% in alloys of the present invention,manganese acts as a ferritic former, thus the levels of manganese insome embodiments of the alloys of the present invention are controlledfrom about 22.0 to about 25.0 wt-% with other embodiments in the rangeof about 22.0 to about 23.0 wt-%.

Nitrogen is beneficial to austenitic stainless steels because itenhances pitting resistance, retards the formation of thechromium-molybdenum sigma phase, and increases yield strengths of thesteels. Nitrogen in solid solution is the most beneficial alloyingelement for promoting high strength in austenitic stainless steelswithout negatively affecting their ductility and toughness properties solong as the solubility limit of nitrogen in the austenite is notexceeded. If the solubility limit is exceeded, Cr₂N precipitates and/orgas porosity formation takes place, which deteriorates corrosionresistance, ductility and toughness. Thus embodiments of the alloys ofthe present invention limit nitrogen content to about 0.75 to about 1.00wt-% while other embodiments are in the range of about 0.75 to about0.90 wt-% nitrogen. Further embodiments incorporate from about 0.78 toabout 0.90 wt-% nitrogen.

Chromium is important in the alloys of the present invention for severalreasons. For good corrosion resistance high chromium content is needed.Chromium is the element essential in forming the passive film. Whileother elements can influence the effectiveness of chromium in forming ormaintaining the film, no other element can, by itself, create thisproperty of stainless steel. For high corrosion resistance values, thechromium content of the alloys of the present invention should be atleast about 19.0% by weight. Chromium increases the nitrogen solubilityboth in the melt and in the solid phase and thereby enables an increasednitrogen content in the alloy. High chromium content also contributes tostabilizing the austenite phase against martensite transformation. Onthe other hand, because chromium is a ferrite stabilizing element, thepresence of very high percentages of chromium, will lead to the presenceof ferromagnetic ferrite. To maintain the paramagnetic properties of thealloys of the present invention, the chromium content in someembodiments is about 19.0 to about 23.0% by weight, while in otherembodiments the chromium content is in the range of about 19.0 to about21.0 wt-%. Further embodiments incorporate chromium in the range ofabout 19.0 to about 20.0 wt-%.

Nickel, after carbon and nitrogen, is the most effective austenitestabilizing element. Nickel increases austenite stability againstdeformation into martensite and increases yield strength, toughness, andthe pitting corrosion resistance of the material. Nickel makes ferriticgrades of stainless steels susceptible to stress corrosion cracking inchloride solutions; however in austenitic stainless steels, nickel iseffective in promoting repassivation. U.S. Pat. No. 6,454,879 teachesthat nickel should be restricted to levels below the level in the alloysof present invention, preferably below 0.96 wt % for sufficiently goodcorrosion characteristics. Contrary to this teaching, it has beensurprisingly found that about 1-2 wt-% nickel is necessary to optimizethe ability of the alloys of the present invention to passivate.However, in order to decrease the active corrosion rate, a minimum ofabout 2.7 wt-% (preferably a minimum of about 3 wt-%) nickel is needed.

In alloys of the present invention, nickel improves the critical pittingcorrosion potential of the alloy in neutral solutions at roomtemperature to greater than 450 mV in 80,000 ppm chloride solution. Thisvalue is higher than all commercially available Cr—Mn—N austeniticstainless steels. In alloys of the present invention, a minimum of about2.70 wt-% nickel is necessary to achieve the austenitic structure andallow a high enough Mo content in the alloys to maximize the corrosionresistance properties of the alloys of the present invention. Highnickel content in the alloys of the present invention is needed toprotect the austenitic structure from formation of delta ferrite orsigma phase. Thus, some embodiments of the alloys of the presentinvention incorporate nickel from about 2.70 to about 5.00 wt-% whileother embodiments incorporate from about 2.70 to about 4.25 wt-% nickel.Further embodiments incorporate about 2.75 to about 4.20 wt-% nickelwhile even further embodiments incorporate about 3.50 to about 4.20 wt-%nickel.

Molybdenum in combination with chromium is very effective in terms ofstabilizing the passive film in the presence of chlorides. Molybdenum isespecially effective in increasing resistance to the initiation ofpitting and crevice corrosion. However, the amount of molybdenum thatcan be added to austenitic stainless steels is limited by the onset ofsigma and chi phase precipitation, which embrittle the alloys and reducepitting resistance. Nitrogen additions to molybdenum-free austeniticstainless steels improve pitting resistance; however, the effect ofnitrogen is significantly enhanced in the presence of molybdenum. Thecombined beneficial effects of nitrogen and molybdenum are used inalloys of the present invention to increase resistance to pittingcorrosion and to achieve a higher Critical Pitting Potential compared tocommercially available Cr—Mn—N austenitic stainless steels. However,molybdenum is a strong ferrite former and its content must becontrolled. For purposes of exploiting the beneficial effects ofmolybdenum without formation of any ferrite material, the molybdenumcontent of some embodiments of the alloys of the present invention isrestricted to about 1.35 to about 2.00 wt-% while other embodimentsincorporate about 1.40 to about 1.80 wt-% molybdenum. Even furtherembodiments have molybdenum concentration of about 1.40 to about 1.75wt-%.

Copper affects the metallurgical stability in the alloys of the presentinvention. Copper is an austenitic stabilizer and is added to aid theparamagnetic properties of the alloys of the present invention. Copperup to a maximum of about 1.00 wt-% is beneficial in terms of itspassivating ability, pitting corrosion resistance, and active corrosionrate. U.S. Pat. No. 6,454,879 teaches that copper in Cr—Mn—N austeniticsteels should have a maximum of about 0.3 w-t % and preferably less thanabout 0.25 wt-% in order to achieve a desired degree of corrosionresistance. In contrast to previous teachings, it has been surprisinglyfound, that a copper content of at least about 0.35 wt-% achieves thebest corrosion properties. Thus, copper is present in some embodimentsof the alloys of the present invention in amounts of about 0.35 up toabout 1.00 wt-%, and in other embodiments copper is present in about0.35 to about 0.85 wt-%. Further embodiments have a copper concentrationof about 0.35 to about 0.75 wt-% with an even further embodiment havinga copper concentration of about 0.50 to about 0.75 wt-%.

Boron is added to the alloys of the present invention in order toincrease the intergranular corrosion resistance and pitting resistanceof the alloys of the present invention. At too high a boron content, thecorrosion resistance may be deteriorated. Therefore, the boron contentin some embodiments of the alloys of the present invention is about0.002 to about 0.006% by weight. Boron levels in other embodiments areabout 0.003 to about 0.006 wt-%. At these levels, the boron will be insolution and provide beneficial effects on the pitting resistance. Boronalso retards (Cr₂)₃C₆ precipitation and therefore has a beneficialeffect on the intergranular corrosion resistance of the alloys of theinvention.

Sulfur, especially in high manganese stainless steels, affects thecorrosion resistance negatively by forming easily soluble sulfideinclusions. The morphology and composition of these sulfides can have asubstantial effect on corrosion resistance, especially pittingresistance. Therefore, the sulfur content of the alloys of the presentinvention is limited to a maximum of about 0.01 wt-% in someembodiments. Other embodiments contain a maximum of about 0.006 wt-%sulfur. Sulfur contents of even further embodiments are about 0.003wt-%.

Enrichment of Phosphorus together with chromium at the grain boundariescan form Cr—P compounds. Formation of Cr-rich phosphides can deplete thenearby region of Cr and cause intergranular corrosion. Therefore it isimportant that alloys of the present invention contain a minimum amountof phosphorous. Some embodiments of the alloys of the present inventioncontain up to about 0.030 wt-% phosphorous while other embodimentscontain up to about 0.025 wt-% phosphorous. Still further embodimentscontain up to about 0.020 wt-% phosphorous.

EXAMPLES

A series of heats per alloys of the present invention were melted, andthe bars were forged and tested for yield strength, tensile strength,elongation, reduction of area, and impact toughness. The composition ofthese heats are reported in Table 1 while the mechanical properties arereported in Tables 2 and 3. Tables 1-3 also compare various propertiesof alloys of the present invention with those of commercially availablesteels. As shown, the alloys of the present invention met the desiredcombination of properties for higher yield strength, higher pittingcorrosion resistance, maintaining nonmagnetic permeability, andresistance to intergranular corrosion. All the foregoing samples met thedesired criteria for magnetic permeability, yield strength, improvedpitting corrosion resistance, interangular corrosion resistance, minimumhardness, and notch impact strength as set forth above.

TABLE 1 Chemical Composition (wt-%) and PREN Sample Material C Mn Cr NiMo N Cu Si S B P PREN A (2G237) J38 0.016 22.08 19.55 2.73 1.74 0.8190.35 0.38 0.003 0.006 0.020 38.40 B (2G542) J38 0.027 22.20 19.38 3.661.47 0.798 0.60 0.33 0.001 0.003 0.010 37.00 C (1P880) J38 0.024 22.4619.71 3.91 1.44 0.843 0.52 0.30 0.002 0.004 0.011 37.95 D (2G695) J380.024 22.18 19.65 4.18 1.53 0.800 0.55 0.35 0.002 0.004 0.013 37.50 1P580 0.040 23.70 21.60 1.93 0.36 0.860 0.12 0.19 0.003 0.001 0.018 36.552 Datalloy2 0.032 14.50 14.99 2.33 2.56 0.382 0.17 0.20 0.006 0.0030.015 29.55 3 P550 0.050 20.44 18.89 1.44 0.48 0.711 0.03 0.17 0.0030.001 0.016 31.84 4 NMS140 0.025 19.67 18.18 1.78 0.97 0.63 0.11 0.380.002 0.003 0.025 31.51 Materials A-D are the alloys of the presentinvention Materials 1-4 are commercially available materials 1 = steelof U.S. Pat. No. 6,454,879 2 = steel of PCT Publication No. WO 99/232673 and 4 = commercially available

TABLE 2 Mechanical Properties Bar Yield Yield Tensile Tensile ReductionImpact Impact Diameter Strength Strength Strength Strength Elongation ofArea Toughness Toughness Sample Material (in.) (ksi) (MPa) (ksi) (MPa)(%) (%) (ft-lbs) (J) A (2G237) J38 11 167 1151 179 1234 22.0 69 120 183B (2G542) J38  8¾ 144 993 166 1145 27.0 69 139 188 C (1P880) J38 10 1481020 169 1165 26.0 70 125 169 D (2G695) J38 10 144 993 163 1124 27.0 73147 199 1 P580  5½ 165 1138 180 1241 23.0 66 62 84 4 NMS140 11 143 986163 1124 24.0 70 125 169

TABLE 3 Critical Pitting Potential and CP Temperature 50 100 200 CPTSample Material (μA/cm²) (μA/cm²) (μA/cm²) (° C.) B (2G542) J38 584 642720 54.5 1 P580 250 344 408 — 2 Datalloy2 −20 −12 6 — 3 P550 −50 −14 18<10 (1.9) 4 NMS140 −29 −14 2 14.6

Critical Pitting Potential (CPP)

The test procedures used for this test followed the guidelines of ASTM G5, Standard Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization Measurements.

The test specimens were placed into a deaerated 80,000 ppm chloridesolution buffered to 6.8-7.0 pH with a borax buffer at ambienttemperature. A saturated calomel electrode (SCE) was used as thereference electrode and platinum mesh as the counter electrode. The testspecimens were allowed to equilibrate with the test solution for 1 hourprior to initiation of the test. Starting with −600 mV vs. SCE, thepotential was increased at a rate of 0.1 mV/s.

Critical Pitting Temperature (CPT)

The critical pitting temperature (CPT) was determined in accordance toASTM G 150, Standard Test Method for Electrochemical Critical PittingTemperature Testing of Stainless Steels. Specimens were placed in a 1molar solution of NaCl in a cell with a calomel reference electrode anda platinum counter electrode. The solution was aerated in air and apotential of +700 mV was applied between the sample and the referenceelectrode. The temperature was increased at 1° C./min. The CPT wasdetermined to be the temperature at which a current density of 100μA/cm² was observed.

All of the U.S. patents, U.S. patent application publications, U.S.patent applications, foreign patents, foreign patent applications andnon-patent publications referred to in this specification and/or listedin the Application Data Sheet are incorporated herein by reference, intheir entirety.

While particular steps, elements, embodiments and applications of alloysof the present invention have been shown and described herein forpurposes of illustration, it will be understood, of course, that theinvention is not limited thereto since modifications may be made bypersons skilled in the art, particularly in light of the foregoingteachings, without deviating from the spirit and scope of the invention.Accordingly, the invention is not limited except as by the appendedclaims.

1. An austenitic, paramagnetic material with high strength, ductility,and yield strength and good corrosion resistance in media with highchloride concentrations, comprising (in wt-%): up to about 0.035 carbon;about 0.25 to about 0.75 silicon; about 22.0 to about 25.0 manganese;about 0.75 to about 1.00 nitrogen; about 19.0 to about 23.0 chromium;about 2.70 to about 5.00 nickel; about 1.35 to about 2.00 molybdenum;about 0.35 to about 1.00 copper; about 0.002 to about 0.006 boron; up toabout 0.01 sulfur; up to about 0.030 phosphorous; and substantially noferrite content.
 2. The material according to claim 1, wherein thematerial comprises about 2.70 to about 4.25 wt-% nickel.
 3. The materialaccording to claim 2, wherein the material comprises about 2.75 to about4.20 wt-% nickel.
 4. The material according to claim 3, wherein thematerial comprises about 3.50 to about 4.20 nickel.
 5. The materialaccording to claim 1, wherein the material comprises about 0.35 to about0.85 wt-% copper.
 6. The material according to claim 5, wherein thematerial comprises about 0.35 to about 0.75 wt-% copper.
 7. The materialaccording claim 6, wherein the material comprises about 0.50 to about0.75 copper.
 8. The material according to claim 1, wherein the materialcomprises (in wt-%): up to about 0.030 carbon; about 0.25 to about 0.45silicon; about 22.0 to about 23.0 manganese; about 0.75 to about 0.90nitrogen; about 19.0 to about 20.0 chromium; about 2.70 to about 4.25nickel; about 1.40 to about 1.80 molybdenum; about 0.35 to about 0.75copper; about 0.003 to about 0.006 boron; up to about 0.006 sulfur; andup to about 0.025 phosphorous.
 9. The material according to claim 8,wherein the material comprises (in wt-%): up to about 0.028 carbon;about 0.30 to about 0.45 silicon; about 22.0 to about 23.0 manganese;about 0.78 to about 0.90 nitrogen; about 19.0 to about 20.0 chromium;about 3.50 to about 4.20 nickel; about 1.40 to about 1.75 molybdenum;about 0.50 to about 0.75 copper; about 0.003 to about 0.006 boron; up toabout 0.003 sulfur; and up to about 0.020 phosphorous.
 10. The materialaccording to claim 1, wherein the material has a PREN value of greaterthan about
 37. 11. The material according to claim 10, wherein thematerial has a PREN value of greater than about 37 and less than about39.
 12. The material according to claim 1, wherein the material has ayield strength at 0.2% offset of greater than about 140 ksi.
 13. Thematerial according to claim 12, wherein the material has a yieldstrength of greater than about 140 and less than about 190 ksi.
 14. Thematerial according to claim 1, wherein the material has a PREN value ofgreater than about 37 and a yield strength at 0.2% offset of greaterthan about 140 ksi.
 15. The material according to claim 14, wherein thematerial has a PREN value of greater than about 37 and less than about39 and a yield strength at 0.2% offset of greater than about 140 andless than about 190 ksi.